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Re: [Xen-devel] [PATCH v9 12/28] ARM: vGIC: advertise LPI support

Hi Stefano,

On 22/05/17 23:19, Stefano Stabellini wrote:
On Tue, 16 May 2017, Julien Grall wrote:
@@ -436,8 +473,26 @@ static int __vgic_v3_rdistr_rd_mmio_write(struct vcpu
*v, mmio_info_t *info,
     switch ( gicr_reg )
     case VREG32(GICR_CTLR):
-        /* LPI's not implemented */
-        goto write_ignore_32;
+    {
+        unsigned long flags;
+        if ( !v->domain->arch.vgic.has_its )
+            goto write_ignore_32;
+        if ( dabt.size != DABT_WORD ) goto bad_width;
+        vgic_lock(v);                   /* protects rdists_enabled */

Getting back to the locking. I don't see any place where we get the domain
vgic lock before vCPU vgic lock. So this raises the question why this ordering
and not moving this lock into vgic_vcpu_enable_lpis.

At least this require documentation in the code and explanation in the commit

It doesn't look like we need to take the v->arch.vgic.lock here. What is
it protecting?

The name of the function is a bit confusion. It does not take the vCPU vgic lock but the domain vgic lock.

I believe the vcpu is passed to avoid have v->domain in most of the callers. But we should probably rename the function.

In this case it protects vgic_vcpu_enable_lpis because you can configure the number of LPIs per re-distributor but this is a domain wide value. I know the spec is confusing on this.


Julien Grall

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